The present invention relates to the production and preparation of single crystalline cubic silicon carbide layers.
Interest in cubic silicon carbide as a semiconductor material is due to the high electric mobility and to the large field of existence of this crystal modification of silicon carbide. According to W. F. Knippenberg, THESIS; Philips Research Reports 18, 161-274(1963), cf. p. 271, the field of existence of cubic silicon carbide extends from 1,000.degree. C. to 2750.degree. C. Unfortunately the preparation of layers of cubic SiC by chemical vapor deposition (CVD) at relatively low temperatures is hampered by the lack of substrates with suitable lattice dimensions and thermal expansion coefficients. Large single crystals of cubic SiC are not available. The growth on silicon substrates is delicate because of large differences in lattice constants and thermal expansion coefficients. Growth on diamond is prevented by the graphitization of the diamond at about 1100.degree. C.
It must be noted, however, that in the preparation of hexagonal SiC by the Lely technique (a high temperature evaporation technique most often used to get hexagonal crystals of silicon carbide) cubic silicon carbide layers are often formed on the surface of hexagonal SiC plates. J. A. Lely and F. A. Kroger (see Semiconductors and Phosphors, Interscience, N.Y. 1958, p. 516) studied the optical transmission of a hexagonal Lely crystal having a cubic overgrowth 30 microns thick (more than is required for the making of electron devices), and Knippenberg (1. cit. pp. 263-266) prepared hexagonal crystals with cubic overlays whose dimensions reached 7 mm diam., and 0.5 mm thickness, by bringing the Lely furnace to about 2700.degree. C., allowing the growth of hexagonal crystals (a lengthy process) and then quickly cooling the furnace.
However, no routine technique exists to prepare very pure cubic silicon carbide layers and devices.